[mythtv] Random blockiness that probably isn't CPU or PCI bus bandwidth-related

Eric Anderson rico99 at sbcglobal.net
Tue Jan 18 20:56:49 EST 2005


Doug -

No. The "bad" recording is corrupt -- if you play it you get MPEG 
playback errors, etc. Blockiness,
choppiness, whatever you want to call it. In most cases it makes it 
pretty much un-watchable.
By comparison, a "good" recording plays back without errors, and does 
not have duplicated
packets (other than PAT, PMAP kind of stuff).

The duplicated packets are anywhere from ~750 to ~1150 packets away 
from each other.
(But remember, this is *after* filtering out only the program being 
recorded, etc. If I were saving
*all* of the packets, maybe I would see a more regular separation. I 
don't know.)

Also, the duplication is not centered around the GOP frames in any way. 
It's just that the GOP
frames are the only *easy* way I have of determining what data should 
be where. The other
packets do not have sequence numbers (that I know where to find at 
least).

I see runs of duplicates anywhere from 6 packets to 130 packets in a 
row. And by looking at
the GOP sequence numbers, I can "guess" that it's not just that 
something was repeated,
something else got squashed (consistent with a ringbuffer problem).

Note: This could also be a cache coherency thing, or PCI thing, CX8800 
hw bug, etc, etc...

-Eric


On Jan 18, 2005, at 5:08 PM, Doug Larrick wrote:

> Eric Anderson wrote:
>> So yesterday I wrote a small program to scan through the saved
>> transport stream to try to figure out *how* the data was corrupted.
>> What I found is sets of duplicate packets. Thus, I am starting to
>> think that this is a driver issue.
>
> Just out of curiosity... do the duplicate packets also have duplicate 
> sequence numbers, and do they immediately follow one another?  If so, 
> it  *could* be your station broadcasting duplicates on purpose for 
> better error recovery.  If I were going to do so for video, I'd do it 
> on the GOP frames.
>
> -Doug
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